1. Field of the Invention
The present invention relates to a zoom lens and image taking apparatus. More particularly, the present invention relates to a zoom lens and image taking apparatus of which a size of the entirety can be small by reduction of a diameter of lens optics.
2. Description Related to the Prior Art
Digital still cameras are widely used, which are a small type with a small thickness, and are portable for carrying. Even in the digital still camera, an optical zoom assembly is incorporated in addition to digital zoom control in which images are zoomed digitally by image processing.
A zoom lens as optical zoom assembly for use in the digital still camera of a small thickness type is constructed so that object light is reflected in a prism or the like to focus an image on a light receiving surface. Also, JP-A 2000-131610 discloses the zoom lens of a path bending type in which a zoom ratio is 3 times or so.
The zoom lens of a reflection type is disposed to bend a path of object light by reflection in a direction vertical to a thickness direction of the digital still camera. Also, an image pickup device such as a CCD is disposed behind the zoom lens and vertically to the thickness direction of the digital still camera. The thickness of the digital still camera of a thin type is determined by a diameter of lenses/lens groups included in the zoom lens and a size of a sensor package of the image pickup device.
Also, U.S. Pat. No. 5,363,163 (corresponding to JP-A 5-005839) discloses a viewfinder optical system for a single lens reflex camera, in which the object light is reflected to bend a path and an image is zoomed. According to this, a zoom relay lens is used for forming an observable image by reducing a size of an intermediate image formed by a taking lens.
In the zoom lens of a known type, the aperture stop control device is disposed in a position away from a first one of the lenses/lens groups located on the object side, namely on a second one of the lenses/lens groups or behind the same. A distance from the aperture stop control device to the first lens/lens group on the object side is considerably great. Specially in the zoom setting in the wide-angle end position, a chief ray height of the first lens/lens group on the object side is very great. Therefore, the first lens/lens group, a prism for reflecting the object light, and other elements must be formed in a relatively large size according to the chief ray height. On the other hand, the size of the first lens/lens group, prism and other elements has not been a factor influencing to reduction of the thickness of the digital still camera, because their size is approximately equal to a size of the sensor package of the image pickup device.
However, a size of the sensor package of the image pickup device has been smaller and smaller in the technical development. A diameter of the lenses/lens groups included in the zoom lens is a bottleneck against the reduction of the thickness of the digital still camera. Reduction of a diameter of the lenses/lens groups included in the zoom lens has been desired strongly.
If it is conceived to use a relay lens of the viewfinder optical system also in an image taking optical system, a general size of the zoom lens is determined according to a size of the intermediate image. There is a problem in that the size of the entirety of the zoom lens must be larger than a sensor package of the image pickup device. A size of the intermediate image may be several times as large as a size of the light receiving surface when the relay lens of the viewfinder optical system is used in the image taking optical system to reduce the intermediate image in the size for refocusing. A diameter of the zoom lens may be larger instead of being smaller.